Perennial Care Guide

Caring for Perennials

More often than not when people think of color or seasonal interest in the landscape, annuals come to mind. In Texas SmartScape, our focus for seasonal color and foliage is on perennials, those plants that return on the same root system from one year to the next.

We feel that perennials make sense. They offer variety and diversity, blooming cycles for 7-8 months of the year, as well as foliage that is rich in color, texture and shape. They also make economic sense in that they do not have to be replanted every year as do annuals.

Although many very low maintenance perennials are available, (many of these are outlined in this web site) most perennials require some maintenance to perform at their best. In this section we will attempt to outline the primary maintenance consideration for perennials.

Deadheading and Shearing

"Deadheading" is the removal of dead flower heads. This process should be performed to encourage the production of new flowers rather than seed. Although deadheading is not strictly required, the procedure can lengthen and intensify a perennial's bloom season.

"Shearing" is the cutting back of a plant all over. Shearing stimulates new growth. Many perennials benefit from this process. Some perennials such as the larger salvias, native Texas aster and Mexican mint marigold will benefit from shearing back one third to one-half at mid-season to keep them dense and encourage strong late-season bloom.

Fertilizing

Most perennials do not require large amounts of fertilizing. In fact, many will respond to over-fertilization by becoming excessively tall and produce minimal or no flowers. Assuming that bed preparation has been performed as outlined above using a 4" to 5" depth of organic compost, most perennials will need minimal to no additional fertilizer during the first year of growth.

Top dressing with compost appears to be the best method for providing sufficient nutrients for perennials. Generally, top dressing should take place in mid to late February. Use a 1" to 1.5" depth of compost every two to three years. Take care to scratch or incorporate the compost lightly into the soil.

The object is to improve the soil and its organic content so that nutrients are readily available for the plants.

If you cannot invest in the labor and/or material to accomplish top dressing with compost, then consider feeding with compost, organic fertilizer (composted poultry or cow manure, cottonseed meal, etc.) or sulfur-coated, slow-release synthetic fertilizers. If you do use synthetic fertilizer, work the fertilizer lightly into the soil or apply below the mulch layer so that there is less likelihood of it being washed into storm drains by heavy rains or excessive watering.

If you feel the need to use supplemental fertilizer, these applications should be made during the period March through September. Fertilizer needs and rates of application ideally should be based on soil tests. If you cannot perform timely soil tests, apply according to fertilizer labels approximately every 60 to 90 days. There are some perennials that are heavy feeders (e.g., phlox, daylilies, daisies, hibiscus) and they can benefit from being fed approximately every 45 to 60 days during the March-September time frame.

To recap, proper initial preparation of beds with organic matter is key to the future health and fertilization regime with regard to perennials. If the soil is rich and well prepared, little or no supplemental fertilizer is required for most perennials. Top dressing with a 1" to 1.5" depth of a good aged compost every 2 to 3 years is the best approach to providing nutrients to most perennials.

Pests and Disease

Usually few major pest and disease problems will arise in perennial gardens if the right plant has been chosen for the right place. That is to say, choices of acclimated plants for the correct cultural matches (light requirements, drainage, soil type, root competition, etc.) will result in little or no major pest and/or disease problems. Hopefully, by using the SmartScape plant database you will be well on the road to choosing the right plant for the right spot.

Monthly inspections for insects, diseases and over/under watering will keep you aware of potential problems. Just seeing several insects on a plant does not mean you have a problem; they may be beneficial insects. Observe the details of their appearance and make written notes. Next use an expert or a reference (county extension agent, nursery, gardening book, etc.) to identify the insect and determine if treatment is necessary.

Even the presence of a number of harmful insects won't cause significant, lasting damage, if a sufficient number of predators are present to consume them. If treatment is required, apply least toxic materials (including the use of bacterial sprays and organic methods).

Planting

Carefully evaluate the drainage of the area to be planted. If a site does not drain, it will not support healthy plants. Poorly drained soil is responsible for more plant failure than any other single cause. One way to check the percolation of the soil is to dig a hole approximately 2 feet deep and fill it with water. Let the water drain away and then refill the hole. If the water drains away twice within an hour, the soil is well drained and will support most any plant that insists on impeccable drainage. (e.g., Calylophus). If the water drains within 6 hours, it is suitable for plants that will accept heavy soil (e.g. Canna, Flame Acanthus). If water stands beyond six hours-consider building a raised bed or install a subsurface French drainage system (perforated pvc pipe in a gravel bed), or planting plants that tolerate poor drainage.

Prepare the soil by excavating as necessary to remove all weeds and grass. Preparation may require a 3" to 4" depth be removed in a heavily infested area (especially in Bermuda lawn grasses). In areas which are clear where no grass or weeds exist, no excavation is necessary, next add a 4"-5" depth of organic material (compost) to the soil in the area to be planted. Rototill or fork the organic matter into the existing soil to a depth of 4" to 5". This procedure provides an 8" to 10" prepared planting zone.

Rake out the beds to remove all debris and to smooth the grade. Also, grade the beds so that a crown exists (higher in the middle). Grading to a crown will help to ensure positive drainage in the planting bed.

Lightly moisten the prepared areas before planting begins. Determine the proper spacing for the mature size of the plant (refer to the plant selection database to detemine the width of the plant). Lay out the plants, still in pots, on the ground and make any adjustments according to individual preferences and site lines.

Start planting. If roots are matted or pot-bound, rip the outer edges of the root systems so that the roots will grow outward. Set the plants level with the surrounding soils, (i.e., plant so that the top of the root ball is even with the surrounding soil). Setting plants too low will cause drowning and/or rotting.

Water the plants thoroughly. Add a layer of mulch to the beds using a 1" to 2" depth of organic material. (e.g., shredded hardwood, cypress, compost). Add additional mulch as needed to maintain a 1" to 2" layer. (Generally twice a year-early spring and early winter).

Staking

One way to avoid having to stake perennials is select shorter-growing varieties or to choose those that are self-supporting. Unfortunately, sometimes staking is unavoidable in order to keep some perennials from "eating" their neighbors alive (e.g., Mexican Bush Sage. Ox-eye Daisy, Lindheimer's Gaura).

If staking needs to be done, do it early. (All you tomato growers know what we mean.) The stems of the plant need to be sturdy and flower buds should not be formed yet. Stakes placed early are easily hidden by subsequent maturing foliage.

Use natural materials (for example, bamboo or branches) whenever feasible. Use ties such as jute or string that blends well and are biodegradable. Don't tie the stems of plants so tightly that they look restricted.

Transplanting & Thinning

Perennials, in general, should be transplanted during the season opposite of when they bloom. That is, transplant spring and summer flowering perennials in the fall and transplant fall flowering perennials in the early spring.

It is best to cut back the plant by at least one-half to two-thirds before transplanting. Cool, rainy or overcast days are the best time to transplant. Be sure to water the plant before moving it and the soil into which you are transplanting. Use a sharp shovel and keep as much root ball as possible. Water in the transplant immediately. Plants may need to be shaded for several days if transplanting is done during a period of high temperature.

Most perennials will give you signs when thinning or division is in order. Telltale signals are the flowers get smaller over the years; a clump may take on the appearance of a tangled up mess; the plant may develop a hole in the center; the plant may in general have less vigor; the plant tends to flop over as it ages or the plant my be spreading aggressively.

Watering

Water only when the plants need it. Do not water on a fixed schedule. Let the plants dry out between waterings (don't let them get bone-dry or wilted). Probe the soil and if it is dry in the top 4" to 5"; then it is time to water.

Remember, plants may show the same symptoms from being over watered as being under watered (e.g., yellow leaves and/or wilting). There is no other way to determine when a plant needs water other than to monitor the soil moisture. Water perennials separately from lawns if you are using an automatic watering system. Early morning is the best time of the day to water. Late evening or nighttime watering may encourage mildew and or fungus. Water deeply. A general rule of thumb is to provide (from rainfall and irrigation combined) a 1" to 2" depth of water every week in the summer; 1" to 2" depth of water every two weeks in the fall and spring and 1" to 2" per month in the winter. Use a rain gauge to determine how much water is being applied.

Pay attention to seasonal variations. When changing over from spring to summer, for example, the quick cutoff of all rainfall can be brutal to plants. Watch out for both over and under watering in the winter months.

Winter Protection

After a frost has "hardened off" perennials, it is helpful to add mulch (1" to 2" layer). Do not mulch too early or the mulch may encourage new growth which can be killed by a sudden hard freeze. Prune woody perennials back after a light frost has hardened off the plant. This process will reduce the exposure to hard freezes. Herbaceous perennials, in general, should be cut back as late as possible (mid to late February) so that pruning will not stimulate new growth which may be killed by late winter, hard freezes.

Water perennials deeply before a hard freeze is expected. This watering will protect roots, which may be exposed to cold air pockets in the soil and will help prevent plant tissue dehydration from cold, dry winds.

Checking the soil is the only fail safe way to know when to water.

Leave it on the lawn! Yard clippings can pollute nearby streams and creeks.

Texas SmartScape™ is helping to promote education on pollution prevention through efficient and effective water use for the benefit of all citizens.

A Program of the North Central Texas Council of Governments, Regional Stormwater Management Coordinating Council.